Combined bacterial/metal catalysis turns sugars to jet fuel

Reactions operate near theoretical efficiencies to make long hydrocarbons.

The clear liquid on top contains butanol and acetone, while the opaque gloop at the bottom contains the bacteria that made them.

Robert Sanders photo.

Although battery-powered vehicles are making great strides, it's tough to match the energy densities found in hydrocarbons. So they'll always be an excellent choice for applications where weight or long distances are involved—think airplanes and ships—but our planet has a finite supply of easy-to-extract hydrocarbons. At some point, we'll inevitably need to look for alternatives.

Biofuel is one option with some appeal. Fossil fuels, after all, are simply the result of a bit of time and geology acting on plant matter. We should, in theory, be able to speed that process. So far, however, the easiest thing to produce has been ethanol, which isn't nearly as energy rich as the hydrocarbons in diesel and jet fuels. But a new process that mixes bacteria with traditional catalysts in a single process provides a relatively high conversion of sugar to hydrocarbons.

The process relies on a specific species of bacteria, Clostridium acetobutylicum. Given a source of sugar (which can be obtained by digesting cellulose in plants), these bacteria will produce a mixture of small carbon compounds: acetone, ethanol, and butanol. Although these chemicals can be useful in a number of contexts, they're not great as fuels. The longest of these is only four carbons, and all of them have an oxygen incorporated into their structure.

Normally, these products of metabolism will build up until they become harmful to the bacteria making them, causing the reaction to shut down. But a team of Berkeley scientists has found a solvent, glyceryl tributyrate that doesn't mix with water. It will preferentially dissolve acetone and butanol, separating them out from the water that the bacteria live in. This also leaves the ethanol behind, possibly for use as a separate biofuel.

Once separated, a simple catalyst (K3PO4 and palladium) can catalyze a condensation reaction. In these reactions the butanol combines with the acetone, releasing a water molecule in the process. The reaction, however, leaves a chemical structure called a ketone behind (a carbon atom double bonded to an oxygen). This is very similar to the structure of the acetone in the first reaction, allowing a second condensation to occur.

The end result is an 11 carbon compound with a ketone in the middle, which accounts for about half of the output of the reaction (the rest is distributed among a mix of other oxygen-containing hydrocarbons). That's not quite a traditional hydrocarbon fuel, but it apparently burns very similarly to diesel fuel. And it can be fed into the existing refinery infrastructure and used as a feedstock for producing either diesel fuel or jet fuel. It's quite a bit more expensive than existing petroleum feedstocks, but their limited supply and the externalities associated with their use will inevitably tip the balance in favor of something like this.

Aside from price, there are a couple of downsides to this process. One is the use of palladium, which is quite expensive. The authors show, however, that each mole of palladium catalyst is good for producing at least 3,000 moles of reaction products before it will need to be recycled. So, this isn't as much of a cost as it appears to be. Plus, it might be possible to find a cheaper catalyst that is just as effective.

The other issue is the complex mix of hydrocarbons that result. Some of these could be potentially useful, as a lot of the materials we use in other products are made by processing petroleum. But they still have to be separated out in various ways before anything can be used—and certainly before this mix is put into a diesel engine.

Even if something better is developed before biofuels really come into their own, the approach demonstrated here is a rather interesting twist. Most efforts so far have focused exclusively on either living or metallic catalysts. By mixing the two, the authors have shown it's possible to tailor a system in which each perform the steps they're best at, and produce a result that's closer to the material we want. In the long run, it's probably better than adapting to an easy-to-make material that's less than ideal.

27 Reader Comments

This article makes me wonder how much research goes into extracting energy from the hydrocarbons in such a way as to reduce their emissions? I would imagine it would be quite a bit of research (as emissions are a huge incentive for alternative energy), but I almost never see any information about new ways to extract energy from hydrocarbons. Any ideas why?

This article makes me wonder how much research goes into extracting energy from the hydrocarbons in such a way as to reduce their emissions? I would imagine it would be quite a bit of research (as emissions are a huge incentive for alternative energy), but I almost never see any information about new ways to extract energy from hydrocarbons. Any ideas why?

Reason for that is generally because we've already spent hundreds of years learning how to use them more efficiently, so there isn't much room for improvement in the first place.

lol, right, because palladium is a cheap and readily accessible resourse!

Here's a better idea, and one we've been doing since WWII: Screw converting sugar to hydrocarbon, just chemically MAKE hydrocarbon from, well, Cabon, H2 gas, and water. We have been doing this for about $15-20 a gallon in small batches for 60 years. We can do it today in highly recouperative systems for approaching $4 a gallon on large scale. It's a near zero waste system (02 is the most "dangerous" byproduct), and the input itself is just carbon, water (40% of which is reused, and need not be pure going into the first stage (the reclaimed water that's pure feeds later stages ensuring no contaminants, but stage 1 is hydrolysis, and that can be done on unclean water, not drinking grade) and energy. The wind industry is suffering from a lack of places to send overproduction of wind and it;s a huge cost drain, and this chemical process can use massively variable loads, so it;s a perfect place to send power solving a key paralel industry problem, and ensuring fuel is carbon neutrally produced. We can make an infinite amount of fuel, and it comes out in a blend similar to refined gasoline (oils, diesel, petrol, jet fuel grades, etc, all easily seperated as we do now in oil refining, except it;s chemically pure with no heavy metals or sulfer). The only reason this isn;t happening is big-oil can;t guarantee control of that industry, and so all forms of grants have been denied to building it out and making it even more cost effective. It is the future.

Converting sugar to hydrocarbon will always be a bad idea as the harvest required will always put strain on the source. The best option is still in researching a way to emulate photosynthesis in order to produce hydrogen or light hydrocarbon. Or we could mine the incredible quantity of waste we produce and convert them to petrolum using thermal depolymerization. In fact we're far better learn how to recycle infinitely resource so when time come we'll be able to survive with a limited set of resource somewhere in deep space.

This article makes me wonder how much research goes into extracting energy from the hydrocarbons in such a way as to reduce their emissions? I would imagine it would be quite a bit of research (as emissions are a huge incentive for alternative energy), but I almost never see any information about new ways to extract energy from hydrocarbons. Any ideas why?

Because, in essence, when you burn a hydrocarbon, you're getting its energy by converting it into these bad emissions. In a perfectly perfect hyrdrocarbon reaction, you've got something like this:

O2 + (CHx)X + boom = CO + CO2 + H20 + energy

Now, of course, real life isn't perfect. A car isn't taking in pure oxygen; it's also taking in a bunch of other stuff that can react to form other bad stuff. But there's only so much you can do to eliminate contaminates (and even then, you're usually doing it AFTER the reaction, in catalytic converters), and at the end of the day you've still got a chemical process that's making all the CO and CO2 completely on its own accord.

In terms of amount of energy you can extract, one of the problems is that while making the energy is easy, capturing that energy and making it useful requires a huge amount of external equipment that reduces the efficiency of energy extraction. Just think about all of the parts there is in a car engine; I think we get something like 35% of the energy from the reaction into propulsion, and that's after 100+ years of development on them.

This article makes me wonder how much research goes into extracting energy from the hydrocarbons in such a way as to reduce their emissions? I would imagine it would be quite a bit of research (as emissions are a huge incentive for alternative energy), but I almost never see any information about new ways to extract energy from hydrocarbons. Any ideas why?

Hydrocarbon-based fuels are already efficient in form and thus contribute to its low cost of consumption. You can tinker on the peripheral by making the devices that utilize these fuels to be more efficient, but you can only extract so much energy from every unit.

As you continue to add additional methods and ways of "safely extracting" energy from this fuel, you add to the costs greatly. This results in very, very expensive consumers of the fuel, even if fuel remains cheaply available. There's a threshold where you come up to a point where even the most wealthiest of your patrons will say, "no mas" and go look for alternative, less clean, devices/products (examples are cars, lawn mowers, and recreational vehicles)

Therefore, it's better to research alternative fuels, scale production up to drive costs down, and then market it to use with existing, cheaper devices/products while also delivering similar energy output AND at "cleaner/safer" levels.

lol, right, because palladium is a cheap and readily accessible resourse!

Here's a better idea, and one we've been doing since WWII: Screw converting sugar to hydrocarbon, just chemically MAKE hydrocarbon from, well, Cabon, H2 gas, and water. We have been doing this for about $15-20 a gallon in small batches for 60 years. We can do it today in highly recouperative systems for approaching $4 a gallon on large scale. It's a near zero waste system (02 is the most "dangerous" byproduct), and the input itself is just carbon, water (40% of which is reused, and need not be pure going into the first stage (the reclaimed water that's pure feeds later stages ensuring no contaminants, but stage 1 is hydrolysis, and that can be done on unclean water, not drinking grade) and energy. The wind industry is suffering from a lack of places to send overproduction of wind and it;s a huge cost drain, and this chemical process can use massively variable loads, so it;s a perfect place to send power solving a key paralel industry problem, and ensuring fuel is carbon neutrally produced. We can make an infinite amount of fuel, and it comes out in a blend similar to refined gasoline (oils, diesel, petrol, jet fuel grades, etc, all easily seperated as we do now in oil refining, except it;s chemically pure with no heavy metals or sulfer). The only reason this isn;t happening is big-oil can;t guarantee control of that industry, and so all forms of grants have been denied to building it out and making it even more cost effective. It is the future.

Well, we're seeing more and more people interested in self-reliance. Instead of siphoning from large-scale infrastructure, they'd rather explore off-grid ideas. This could be something that catches on with the preppers / off-gridders. And, if it takes off there, then it could expand into other markets.

While the financials of large-scale energy production are efficient, I think folks are getting annoyed at businesses controlling the tap, especially since more businesses these days are more interested in shareholder profits than customer service / product. Folks want a sense of control. So, while the industrial revolution was good in bringing lots of folks together, we see the tech revolution helping folks distinguish themselves. I think the house of the future will be fairly self-sustaining; provide its own power, sewage/water recycling, etc. Give folks the ability to have control over those things instead of relying on someone else holding all the control.

lol, right, because palladium is a cheap and readily accessible resourse!

Here's a better idea, and one we've been doing since WWII: Screw converting sugar to hydrocarbon, just chemically MAKE hydrocarbon from, well, Cabon, H2 gas, and water. We have been doing this for about $15-20 a gallon in small batches for 60 years. We can do it today in highly recouperative systems for approaching $4 a gallon on large scale. It's a near zero waste system (02 is the most "dangerous" byproduct), and the input itself is just carbon, water (40% of which is reused, and need not be pure going into the first stage (the reclaimed water that's pure feeds later stages ensuring no contaminants, but stage 1 is hydrolysis, and that can be done on unclean water, not drinking grade) and energy. The wind industry is suffering from a lack of places to send overproduction of wind and it;s a huge cost drain, and this chemical process can use massively variable loads, so it;s a perfect place to send power solving a key paralel industry problem, and ensuring fuel is carbon neutrally produced. We can make an infinite amount of fuel, and it comes out in a blend similar to refined gasoline (oils, diesel, petrol, jet fuel grades, etc, all easily seperated as we do now in oil refining, except it;s chemically pure with no heavy metals or sulfer). The only reason this isn;t happening is big-oil can;t guarantee control of that industry, and so all forms of grants have been denied to building it out and making it even more cost effective. It is the future.

How about you spearhead a kickstarter campaign on this? I'm serious. I'll be a material contributor, and I'll bet you'll get many, many such folks, starting with the Ars crowd.

lol, right, because palladium is a cheap and readily accessible resourse!

Here's a better idea, and one we've been doing since WWII: Screw converting sugar to hydrocarbon, just chemically MAKE hydrocarbon from, well, Cabon, H2 gas, and water. We have been doing this for about $15-20 a gallon in small batches for 60 years. We can do it today in highly recouperative systems for approaching $4 a gallon on large scale. It's a near zero waste system (02 is the most "dangerous" byproduct), and the input itself is just carbon, water (40% of which is reused, and need not be pure going into the first stage (the reclaimed water that's pure feeds later stages ensuring no contaminants, but stage 1 is hydrolysis, and that can be done on unclean water, not drinking grade) and energy. The wind industry is suffering from a lack of places to send overproduction of wind and it;s a huge cost drain, and this chemical process can use massively variable loads, so it;s a perfect place to send power solving a key paralel industry problem, and ensuring fuel is carbon neutrally produced. We can make an infinite amount of fuel, and it comes out in a blend similar to refined gasoline (oils, diesel, petrol, jet fuel grades, etc, all easily seperated as we do now in oil refining, except it;s chemically pure with no heavy metals or sulfer). The only reason this isn;t happening is big-oil can;t guarantee control of that industry, and so all forms of grants have been denied to building it out and making it even more cost effective. It is the future.

If it was really as cheap and simple as you suggest, do you really think 'Big Oil' has such an overarching reach into our economy, that NO-ONE has been able to do it successfully without being interfered with? If so, it really makes you wonder how they've managed to drop the ball so emphatically with all these pesky electric cars getting around.

For starters, could you please name the process you're referring to? What is the carbon feedstock? What is the final product?

lol, right, because palladium is a cheap and readily accessible resourse!

Here's a better idea, and one we've been doing since WWII: Screw converting sugar to hydrocarbon, just chemically MAKE hydrocarbon from, well, Cabon, H2 gas, and water. We have been doing this for about $15-20 a gallon in small batches for 60 years. We can do it today in highly recouperative systems for approaching $4 a gallon on large scale. It's a near zero waste system (02 is the most "dangerous" byproduct), and the input itself is just carbon, water (40% of which is reused, and need not be pure going into the first stage (the reclaimed water that's pure feeds later stages ensuring no contaminants, but stage 1 is hydrolysis, and that can be done on unclean water, not drinking grade) and energy. The wind industry is suffering from a lack of places to send overproduction of wind and it;s a huge cost drain, and this chemical process can use massively variable loads, so it;s a perfect place to send power solving a key paralel industry problem, and ensuring fuel is carbon neutrally produced. We can make an infinite amount of fuel, and it comes out in a blend similar to refined gasoline (oils, diesel, petrol, jet fuel grades, etc, all easily seperated as we do now in oil refining, except it;s chemically pure with no heavy metals or sulfer). The only reason this isn;t happening is big-oil can;t guarantee control of that industry, and so all forms of grants have been denied to building it out and making it even more cost effective. It is the future.

Well, we're seeing more and more people interested in self-reliance. Instead of siphoning from large-scale infrastructure, they'd rather explore off-grid ideas. This could be something that catches on with the preppers / off-gridders. And, if it takes off there, then it could expand into other markets.

While the financials of large-scale energy production are efficient, I think folks are getting annoyed at businesses controlling the tap, especially since more businesses these days are more interested in shareholder profits than customer service / product. Folks want a sense of control. So, while the industrial revolution was good in bringing lots of folks together, we see the tech revolution helping folks distinguish themselves. I think the house of the future will be fairly self-sustaining; provide its own power, sewage/water recycling, etc. Give folks the ability to have control over those things instead of relying on someone else holding all the control.

It just isn't as cheap and simple as he makes it out to be. Electrolysis is a rather inefficient process which itself requires rather expensive catalysts (or else is truly horribly inefficient). Once you have your H2 then you need to use heat and pressure plus CO/CO2 to create mostly methane, which you'll then have to catalytically refine into heavier fuels. All of this MAY be possible as an industrial co-generation type of setup, but stand-alone I'm VERY skeptical it could even close to compete with gasoline price-wise. Then there's the question of how much wind/solar power you can deploy and how fast, and are there just easier and cheaper/more efficient ways to use that energy directly (like charging batteries for example).

Frankly I can't find any numbers on this whole thing, so I refrain from calling BS on the PP's numbers, but I'm quite dubious. Truth is it is amazingly cheap and easy to pull crude out of oil fields. Even these days it costs trivial amounts of money. Oil cos could sell gasoline at a profit for something like $82 cents, maybe less. THAT's the price you have to compete with, not the retail price. Retail is demand set price. Manufacturer wants HIS costs minimized.

Frankly I can't find any numbers on this whole thing, so I refrain from calling BS on the PP's numbers, but I'm quite dubious. Truth is it is amazingly cheap and easy to pull crude out of oil fields. Even these days it costs trivial amounts of money. Oil cos could sell gasoline at a profit for something like $82 cents, maybe less. THAT's the price you have to compete with, not the retail price. Retail is demand set price. Manufacturer wants HIS costs minimized.

You're only off by about a factor of 2. Round estimates for costs to produce a barrel of crude oil is about $80 - $85 USD. If you assume that the barrel of oil gets turned in 42 gallons of gas (not true, it get turns into other products with different prices and there is the 'refinery gain') it comes to about $2.60 / gallon.

And the canonical series of reactions to convert natural gas (or components thereof) to liquid fuels is called the Fischer / Tropsch process. It's been known since the 1920s and has a long a storied history. Several very large industrial plants have recently come on line to convert stranded natural gas into oil products. Given the relatively inexpensive feed stock it seems to be economical, at least in the short to moderate term.

However, starting from carbon, water and oxygen is a whole other, energetically difficult, ball game. Until and unless you have some extraordinarily cheap source of energy, say, the mythical fusion plant, it's not going to work out an commercial scales.

The biggest single killer in ethanol biofuel is the need to separate the ethanol from water. This requires a very energy-expensive distillation, which still leaves excess water (4%) in the ethanol. If one can convert to five carbon alcohols or larger, the low solubility of the organic compound in water allows the separation to be done largely by decanting as an organic and an aqueous layer spontaneously form. Here they add an organic layer, and the more interesting products dissolve in it. Maybe, if the separation problem can be overcome, biofuels will stop being a giant boondoggle, but I am not holding my breath.

A process that depends on palladium and refineries, and uses sugar as a feedstock? Sigh. This is proof-positive that this sector is still very much in heavy R&D mode, trying a bunch of different possibilities, and I don't have high hopes for commercial development.

Producing sugar alone is a massively intensive & dirty agro-industrial process. And then there's the metabolic cost of supporting the bugs themselves.If we want a real viable long-term biofuel solution, I think it will have to use either cellulose or algae (which natively produces high proportions of unoxygenated hydrocarbons) -- both of these processes directly use the photosynthetic biomass, and don't have energy losses from feeding another bioreacting organism.

Cool tech, though. I wonder if all the oxygen-containing hydrocarbons are ketones, or if there are less stable things like ethers in the mix...

Frankly I can't find any numbers on this whole thing, so I refrain from calling BS on the PP's numbers, but I'm quite dubious. Truth is it is amazingly cheap and easy to pull crude out of oil fields. Even these days it costs trivial amounts of money. Oil cos could sell gasoline at a profit for something like $82 cents, maybe less. THAT's the price you have to compete with, not the retail price. Retail is demand set price. Manufacturer wants HIS costs minimized.

You're only off by about a factor of 2. Round estimates for costs to produce a barrel of crude oil is about $80 - $85 USD. If you assume that the barrel of oil gets turned in 42 gallons of gas (not true, it get turns into other products with different prices and there is the 'refinery gain') it comes to about $2.60 / gallon.

No, actually the COST to produce a barrel of crude is on the order of $5 actually. $85 is around the price you'd pay for a contract to deliver it to a terminal in the US, that's a DEMAND price, not a production price. Thus the PRODUCTION COST for a gallon of gasoline is actually far lower, on the order of 80 cents. This is the cost that matters when discussing which is more more expensive to produce. Presumably the DEMAND PRICE you would charge for either good would be the same assuming they're equivalent.

Quote:

And the canonical series of reactions to convert natural gas (or components thereof) to liquid fuels is called the Fischer / Tropsch process. It's been known since the 1920s and has a long a storied history. Several very large industrial plants have recently come on line to convert stranded natural gas into oil products. Given the relatively inexpensive feed stock it seems to be economical, at least in the short to moderate term.

Trust me, I have a degree in chem, I know what Fischer-Tropsch is... What the guy I was responding to was talking about was making 'gasoline' (at least something similar, lets say 8 carbon straight chains), from water, CO2 and electricity. Perfectly feasible but there are a couple steps involved before you get to the Fischer-Tropsch part, which is indeed basically heat, pressure, and a catalyst. The initial creation of methane is actually GENERALLY achieved using steam, not electrolysis by passing steam over coal in the process of coke manufacture. However there is a pathway using CO2, the problem is you have to first GET the CO2 in fairly concentrated form, another energy-intensive process (and usually accomplished by removing it from flue gas). As you can imagine the whole process isn't really all that efficient, or else relies on coal at least indirectly.

[/quote]However, starting from carbon, water and oxygen is a whole other, energetically difficult, ball game. Until and unless you have some extraordinarily cheap source of energy, say, the mythical fusion plant, it's not going to work out an commercial scales.[/quote]

Exactly I don't know where the guy got his "$4 a gallon" number from, but I am skeptical. I suppose perhaps we have some chemical engineering fellows around here who could give us solid numbers. Frankly I suspect it would be better to just store and transport the hydrogen, even though the stuff is a royal PITA to work with.

No, actually the COST to produce a barrel of crude is on the order of $5 actually. $85 is around the price you'd pay for a contract to deliver it to a terminal in the US, that's a DEMAND price, not a production price.

"$5 actually"? Seriously? In the 1970s, maybe, but not today.

Really, folks. If we're gonna argue about facts, let's at least get some to argue about.http://www.eia.gov/tools/faqs/faq.cfm?id=367&t=6The U.S. Government pegs total upstream costs are between ~$17 and $52, depending on location (2007-2009), excluding cost of transportation. That's nowhere near either $5 or $90.

P.s. The oil doesn't find or transport itself, so arguing about what exactly "produce" means is fruitless.

This article brings back the dark high school days studying organic chemistry. Used to be a nightmare for most!As mentioned in the comment, what exactly is the "theoretical efficiency limit" for this process?

And I think you mean "The 'clear' liquid..." for the picture description?

No, actually the COST to produce a barrel of crude is on the order of $5 actually. $85 is around the price you'd pay for a contract to deliver it to a terminal in the US, that's a DEMAND price, not a production price.

"$5 actually"? Seriously? In the 1970s, maybe, but not today.

Really, folks. If we're gonna argue about facts, let's at least get some to argue about.http://www.eia.gov/tools/faqs/faq.cfm?id=367&t=6The U.S. Government pegs total upstream costs are between ~$17 and $52, depending on location (2007-2009), excluding cost of transportation. That's nowhere near either $5 or $90.

P.s. The oil doesn't find or transport itself, so arguing about what exactly "produce" means is fruitless.

Well, first of all my "order of" number is reasonably good, it is pointedly FAR less than the $80+ that is CHARGED for delivered oil (IE what you pay for an oil future, which is what is quoted as 'price'). Also 'cost' is a very slippery thing, a lot of these EIA numbers have to do with amortized costs and capital depreciation, etc. The cost of producing a barrel of oil in CASHFLOW terms is a considerably smaller number. I've heard on the order of $2 for the Saudis, though clearly the total balance sheet is important when talking about comparative costs across industries.

Anyway, the point stands, you don't have to compare the cost of production of synthetic hydrocarbons with the PRICE of refined petroleum products, you have to compare it with the actual source COST of those products. If it costs Chevron $.80 to put a gallon of gasoline in a storage tank at a distributor then the synthetic equivalent has to get to the same tank for the same $.80 or less, otherwise it doesn't compete. Maybe that number is $2 or whatever, but it is some number less than the retail price of gasoline/etc. It is still hard to imagine this synthetic process being cheaper than existing petroleum based products.

A process that depends on palladium and refineries, and uses sugar as a feedstock? Sigh. This is proof-positive that this sector is still very much in heavy R&D mode, trying a bunch of different possibilities, and I don't have high hopes for commercial development.

Producing sugar alone is a massively intensive & dirty agro-industrial process. And then there's the metabolic cost of supporting the bugs themselves.If we want a real viable long-term biofuel solution, I think it will have to use either cellulose or algae (which natively produces high proportions of unoxygenated hydrocarbons) -- both of these processes directly use the photosynthetic biomass, and don't have energy losses from feeding another bioreacting organism.

Cool tech, though. I wonder if all the oxygen-containing hydrocarbons are ketones, or if there are less stable things like ethers in the mix...

Having spent 12 months working in a power generating sugar mill I'm surprised to hear someone describe it as dirty. What form of dirty are you using? Toxic? Nada. Water & heat. CO2? One of the lower emitters of CO2 among the combustible power generators & then you can detract the carbon sinks the plants are. The byproduct waste is locally used as mulch & ground cover.

Compared to the other agricultural industries I've worked in, sugar generation was sterile. If there is a cleaner industry of agriculture I'd be very surprised. I've been in sugar cane, banana & vegetable & exotic fruit farming with minute experiences in more conventional fruit farming & currently learning the cattle industry.

Even if you were referring to the more common uses of dirty, sugar would be among the cleaner farming processes. Porn or hygiene.

Even if you were referring to the more common uses of dirty, sugar would be among the cleaner farming processes.

I would agree with you except for one thing. Every fall when the sugar cane harvest occurs, the cities of Houston and Dallas and the areas of east Texas get covered in smoke from the fires used to burn off the leaves of the sugar cane harvested in Louisiana. That might be the "dirty part". The smoke is a lot more irritating than the oil-saturated air that used to be emitted by the Texas City refineries until the EPA made some noise about it.

Those burnt off leaves along with the stalks from the presses could be used as "feedstock" for bacteria mediated organic fuel production. The leaves could be cut off the stalks instead of burnt. The only reason they're burnt off is to make the stalks stack more tightly in the trailers used to haul the cane to the sugar presses.

There needs to be more attention to details outside of chemistry when detailing alternative energies.